The present invention relates to water-soluble polymers prepared by copolymerization of macromonomers, and to their use in cosmetic and pharmaceutical compositions.
In recent years water-soluble polymers have achieved ever increasing importance in industry and science. In terms of quantity, polyelectrolytes make up a very large part of the overall annual production of water-soluble polymers. They are used as flocculants in paper processing, the detergents industry, textile processing, as protective colloids or, in their crosslinked variants, as thickeners, to name but a few areas of application.
The hygiene sector has become hard to imagine without thickeners, in particular the xe2x80x9csuperabsorbentsxe2x80x9d prepared on the basis of polyacrylic acid, since their development in the 1970s. Newer thickeners, such as, for example, crosslinked polyacrylamidopropylenemethylsulfonic acid (or salts thereof), are notable for their significantly improved pH stability and better processability.
With the aim of simplifying cosmetic preparations, the search has intensified in recent years for raw materials which combine two or more properties in one formulation constituent. Pure xe2x80x9cthickenersxe2x80x9d have been replaced by new substances which, in their property profile, also have emulsifier properties, for example, thus rendering the addition of separate emulsifiers in formulations unnecessary. The synthesis of the polymers described below offers the ideal instrument for this purpose. The interesting combination of a polyelectrolyte (e.g. poly-AMPS) with nonpolar molecular moieties offers the possibility of varying the hydrophilic-hydrophobic balance of a polymer, as has hitherto only been observed in synthetic polymer chemistry in a few cases.
The temperature behavior of the polymers is an important property. Generally, polymers display high viscosity at low temperatures, and low viscosity at high temperatures. However, polymers which have a thickening action above certain temperatures, but remain pumpable and processable in solution at low temperatures, are frequently desired.
EP-A-0 583 814 and EP-A-0 629 649 disclose polymers based on acrylic acid as the main chain and polyethylene and/or polypropylene glycols as side chains. These polymers display thickening at increasing temperatures.
All attempts to produce such polymers on an industrial scale have hitherto been unsuccessful. In addition, the use of acrylic-acid-containing main chain polymers was necessary for realizing the concept of thermothickening polymer solutions in water. One of the most serious problems for this class of polymer are precipitation phenomena based on instabilities toward divalent ions.
In the present invention, then, a novel class of polymer and a process for the preparation thereof are described. Without great preparation costs, using this process based on a free-radical copolymerization, in particular precipitation polymerization, it is possible to prepare a large number of novel polymers with different thermal solution behavior on an industrial scale.
Surprisingly, we have found that polymers which satisfy said requirements can also be synthesized by means of a macromonomer synthesis. The consequence of this is that the stipulation for acrylic acid as one of the main chain monomers, which is required in accordance with the prior art, is unnecessary.